1. Field of the Invention
The present invention relates to an encoding/decoding system adapted to analyze and identify digital input image signals and encode them, and transmit the analyzed and encoded signals to a receiver at which the encoded signals are decoded.
2. Description of the Prior Art
FIG. 1 is a block diagram illustrating an encoder realizing an intellectual encoding according to a prior art disclosed for example in Japanese Patent Public Disclosure (Kokai) No. 7787/89 Official Gazette. In the diagram, numeral 1 is a feature-image-extracting section adapted to extract signals of pixels corresponding to a predetermined feature part in an image from digital input image signals and to output feature signals, 2 a position information detecting section adapted to receive the feature signals from the section 1 and search positions of individual elements constituting the feature part, 3 a position information expressing section adapted to express in numerical values the signals from the detecting section 2 and to output element position signals, 4 a shape information detecting section adapted to receive the feature signals from the section 1 and detect the shape of the elements of the feature part, and 5 a shape information expressing section adapted to express in numerical values the signals output from the detecting section 4 and to output element shape signals.
These signals from the sections 3 and 5 are transmitted to a receiver and decoded.
Operation of the encoder described above will be explained on the assumption that the image represented by the input image signals is a human face as shown in FIG. 2(a) and the predetermined feature part of the face image is a mouth portion as shown in FIG. 2(b).
The extracting section 1 functions to extract the mouth portion encircled by the dotted line in the face image shown in FIG. 2(a), and output mouth part signals as the feature signals to the position and shape information detecting sections 2 and 4. The position information detecting section 2 functions to search actual positions of the respective elements 200 shown in FIG. 2(b), or upper and lower lips on the whole image, and the position information expressing section 3 transforms the signals from the section 2 to signals expressed in the form of absolute coordinates based on the whole frame and outputs the element position signals.
On the other hand, the shape information detecting section 4 functions to analyze the shape of the elements 200 and detect suitable feature points P.sub.0, P.sub.1, P.sub.2 and P.sub.3 which are end points and center points of the elements 200 as shown in FIG. 3. The shape information expressing section 5 operates to detect the coordinate values of the feature points, P.sub.0 (X.sub.0, Y.sub.0), P.sub.1 (X.sub.1, Y.sub.1), P.sub.2 (X.sub.2, Y.sub.2) and P.sub.3 (X.sub.3, Y.sub.3) as shown in FIG. 4(a), and the calculate and output parameters l, p, d and .alpha. of the feature image shape as shown in FIG. 4(b), where l is a length from points P.sub.1 (X.sub.1, Y.sub.1) to P.sub.3 (X.sub.3, Y.sub.3) for representing a mouth size, p and d are relative parameters to express the shape of the mouth image, and .alpha. is an inclination of the line P.sub.1 P.sub.3 from the horizontal line.
According to the intellectual encoder constituted as described above, there has been such a problem that when a new shape not recorded in a memory set in the sections 4 and 5 is detected in the input image, it is impossible to detect such a shape or it is likely to be erroneously detected due to a lack of knowledge for detecting such a shape or a position thereof.
There has also been another problem wherein even if the shape and position of the input image do not change, but if luminance information of pixels (picture elements) constituting the feature image are considerably changed, the output image may be fairly different from the input image when pixel luminance information in the first frame is used for decoding at receiver.
There has been a further problem that since the brightness information of images has to be stored at both of the transmission side and the reception side for every pixel, the utility capacity of the memory is large.
Furthermore, when an object image moves vigorously, it may not be possible to transmit the object image information at a low rate because the amount of brightness information to be transmitted is large.